1. Field of the Invention
The present invention relates generally to an iris identification method and system for acquiring the image of an iris, comparing the image with previously registered information and identifying a person, and, more specifically, to an iris identification method and system, which decompose a person's iris image into a plurality of domains, extract iris code representing the characteristic feature(s) of the respective domains, and storing such iris code in a database, and then identify a person's identity by generating the iris code from the iris image of the person in question in the same way, and comparing this code with the codes stored in the database, thereby improving the speed and accuracy of iris identification.
2. Background Art
There is known a general processing method for identifying a person's identity using the iris, which consist of the following steps: in case of registration, they consist of detecting the iris from overall eye image, dividing iris into a suitably determined domains, generating iris code, storing the codes in a database; and in case of identification, generating the iris code of the person in question, searching the database for iris codes that are closest to the code at hand, and reaching the final decision based on the suitably chosen threshold value.
One of the methods of acquiring specific information from an iris region to perform such a processing method is disclosed in U.S. Pat. No. 5,291,560 filed by John G. Daugman.
In the Daugman patent, a circle with which the boundary between an iris and a pupil is best approximated is searched for, the boundary between the iris and a sclera is approximated with a circle, and the region between these two circles is set to be an iris region. This annular region is further divided by a plurality of ring-like regions based on the equal proportion principle, as shown in FIG. 1(a). The iris code is generated from the each ring-like region by the use of the Gabor transform; this iris code is stored in a database. At the time of person's identification, the same procedures apply to the iris image of the person in question, and in particular, the iris code of the person question is generated. The identification procedure is such that a person in question is identical to a registered person if it is determined that the difference in information falls within a threshold value. However, this method may face a problem because a portion of the iris is typically covered by the eyelids or eyelashes, thereby producing an incorrect iris code that results from the image portion not belonging to the iris proper. This reduces the accuracy of the identification.
In order to cope with this contingency, the Daugman patent presents some remedy. It is based on the observation that the portions of the iris that are directly far above or below the pupil are more likely to be occluded by the eyelids or eyelashes. As a result, the Daugman patent proposes to cut out those portions from the ring-like regions and use the remaining ones. FIG. 1(b) shows the remaining usable portions of the ring-like regions. It then extracts iris code from those portions only. However, this method still has a drawback in that while such usable portions are preset in the a prior manner without regard to individual circumstances, the actual occlusion pattern in each image occurs in endless variety in reality, which means that portions presumed usable in the Daugman patent may very well be occluded in reality. It is clear that the occlusion patterns for the images of same individual differ every time the image is taken, and moreover due to a blink or impurities such as tear drops, the unoccluded iris region varies significantly. All these inaccuracies are likely to seep into the iris code, thereby reducing the accuracy of identification.
Another example of previously well known iris identification technology is disclosed in U.S. Pat. No. 6,247,813 previously filed and registered by some of the present applicants, in which the technology for calculating a plurality of identification parameters for iris identification based on the fiber structure of the iris, the reaction of the pupil and the Autonomous Nervous Wreath (ANW) to light, the shape of the ANW, and the location and shape of a lacuna from the iris image, and identifying a specific person based on the identification parameters is disclosed. The most important feature of this technology is a technique called the variable multi-sector method. In this method, the pupil and iris boundaries are represented by circles, and the region between these two circles is divided into multiple sectors using concentric circles and radial line segments, then suitable frequency transform, such as Haar Transform, is applied to each sectors to generate iris code to be used at the time of registration and identification. The most significant feature of this technology is the use of dynamically determining which sectors to discard and which sectors to use with regard to circumstances of the individual image. The discarded sectors are bad sectors that are occluded by eyelids, eyelashes, or some other impurities, and good ones are those free from such defects. This preceding patent then uses only remaining good sectors to generate iris code at the time of registration and identification. When comparing the two images (in fact codes), only those sector that are deemed to be good in both images (codes) are used in calculating the distance between the two. Therefore, a good sector used at the time of registration does not necessarily participate in the final calculation at the time of identification unless the same sector also turn out to be good in both images. This patent has advantages in that unpredictable contingencies concerning various occlusions that occur at the time of image capture can be efficiently dealt with and thus identification rate is considerably improved.
However, this patent still has several drawbacks. That is, as shown in FIG. 2, there are many cases in which it is difficult to approximate humans' iris boundaries with circles, so that, when an iris boundary is approximated with a circle, a portion of the eye image other than the iris region is inevitably mistaken for the iris region and thus misused, thereby reducing the identification rate. Furthermore, it also has a disadvantage in that the sectors are constructed in a uniform and predetermined manner so that sectors that are only slightly covered with the eyelid or eyelashes must still be considered bad and thus be inevitably discarded, which makes it impossible to utilize the remaining good portion inside the bad, discarded sector.
Moreover, in the Daugman patent, when the iris region is extracted from the iris image captured by the camera, the inner boundary of the iris, which is the boundary between the pupil and the iris, the outer boundary of the iris, which is the boundary between the iris and the sclera, are treated as circles or ellipses for ease of data processing even though they are in reality closer to general curves, and the dividing lines for dividing the iris region into a plurality of sectors are treated as circles. These also put some limitation on the improvement of identification rate because such geometric characteristics cannot be fully utilized.